Almost every day, Marcia Airis drives the winding road of Potomac, a vigilant sentry scanning the castle-like houses and estates.

Airis returns to her sprawling home on most days content that all is well in her village. Occasionally, though, on some rolling lawn, an inconspicuous sign announcing a request for a zoning change will catch her eye and soon she will carry a message to every Potomac mansion and farm: The developers are coming.

The battle will then be joined. On one side, Airis and about 500 other members of the West Montgomery Civic Association reinforced by a battalion of lawyers, planners and traffic engineers. On the other, the proponent of some town house development or shopping center. The conflict might be brief, or it could be fought for years in court, but the outcome will almost always be the same: The developer will lose.

While rampant suburban growth has overwhelmed other small towns in the Washington area, Potomac remains virtually the same as it was 20 years ago, a town of enormous houses on two-acre lots, a wealthy enclave where there are no funeral parlors or halfways houses or fast-food stores, and scarcely any housing for low- or moderate-income families.

That Potomac has stayed that way is no accident. Acting as its guardian is a group of neighborhood activists adept at using all the tools necessary for today's modern development fight -- from zoning to sewer lines to public relations. Even in affluent and sophisticated Montgomery County, where anti-growth is a kind of catechism and citizens groups can usually count on a bevy of lawyers and high level federal officials among its members, Potomac's success is unusual.

Of the 13,348 acres that county planners think of as Potomac, 98.5 percent is zoned for residential use, mostly one house per two acres. In reality, many of the homes are on more than two acres of land, and about one fourth of the land zoned for residential use still is undeveloped.

The only commercial areas in Potomac consist of two inconspicuous neighborhood shopping centers and Montgomery Mall, located on 60 acres on the fringe of town and well away from the Potomac of large houses and estates.

The cost of admission, not surprisingly, is high. In one of the richest counties in the nation, Potomac residents are the wealthiest citizens. The 1978 median household income for Potomac was $39,420 -- more than $8,000 higher than the median income for the county. Many Potomac homes sell for more than $400,000, and the average selling price for a Potomac home this year was $176,961 -- the highest in the county and $76,000 higher than the county average.

Potomac residents say that they fight to keep their village from changing because they purchased their homes knowing that Potomac would be an area of low density and wide lots, a green wedge between transportation corridors, as specified in the 1964 general plan for Montgomery County.

But residents of other towns and villages in the county also purchased their homes knowing that their neighborhoods would be a "wedge." They have not had nearly as much success as Potomac residents in keeping their neighborhoods away from the designs of developers.

During the last 10 years, developers have requested 21 zoning changes in Potomac but have succeeded in only five cases, according to county zoning records. In contrast, developers requested 16 zoning changes in Olney -- another area that was supposed to be a green wedge -- and won 11 of them. Still another area that was supposed to be a wedge, Wheaton, was the target of 24 zoning requests by developers, who won in 18 cases.

Lawyers who represent developers say it is so dificult to win a zoning change in Potomac that they do not even try unless the developer's case is extraordinarily strong. "Looking at a three-to-five-year fight in Potomac is an intimidating factor," said John Delaney, a lawyer for Linowes and Blocher, a Silver Spring firm which has a reputation for getting a developer what he wants. "Developers are more inclined to go to places in Wheaton or Kensington."

One of the main ingredients of Potomac's success, of course, is wealth. Without the money to press the lawsuits and hire the expert witnesses, many of the battles that have been fought in the town would have been lost. But there is more to the story than that.

Over the years, residents of the town have acquired the tactical knowledge of military school graduates. Whether it's heading off adverse development before it's proposed or responding to a specific proposal, the tactics are highly refined and usually successful. Among the more successful are these:

The Law Writing technique. Ellie Lieberman was upset when she learned that an optometrist wanted to sell glasses from his Potomac office, making it look like a store. Lieberman, a housewife, went to the county attorney's office, spent days reading law books, and finally wrote an amendment to a zoning law preventing optometrists from selling glasses in residential offices. The council voted for her amendment.

On another occasion, Lieberman and her civic association were angry when they heard that the Marriott Corporation wanted to build a fast-food restaurant in Potomac. Lieberman then wrote an amendment to a zoning law that prohibited fast-food restaurants in Montgomery County unless the Board of Appeals granted the restaurant a special exception. Marriott was never granted a special exception to build its fast-food restaurant in Potomac.

The Sewer Strategy. Potomac residents like septic tanks and fight against having normal sewer service. The reason: Septic tanks cannot operate on less than two acres of land, making it difficult if not impossible for developers to build at increased density.

Currently, the National Headquarters of the Girl Scouts is asking the County Council to give sewer service to it 88-acre tract of wooded land along MacArthur Boulevard in Potomac. But Potomac residents, who say the land may be sold to a developer, are fighting the request.

Last week, County Attorney Paul McGuckian told council members that the Scouts had every legal right to sewer service. But council members, under pressure from Potomac residents, decided to postpone a decision.

Keeping Cowpaths: Potomac residents have fought successfully against having River Road, Seven Locks Road and Falls Road widened despite huge traffic jams at rush hour. This way cars from other parts of the county are discouraged from driving through their neighborhood.

Also bolstered is the argument when developers try to build in Potomac, that the area cannot take an increase in traffic.

Instant Expertise: Potomac residents are experts at shooting down the arguments of developers, their lawyers, and the experts hired by their lawyers. The reason: Potomac residents are themselves planners, engineers, architects, and lawyers.

The current president of the West Montgomery Civic Association, for example, Ruthann Aron, is a lawyer whose specialty is zoning. Before becoming president of the civic association, she worked as a law clerk for Linowes and Blocher, the law firm that represents most developers in Montgomery County.

If the experts don't live in Potomac, they can usually be found close by.

Three years ago, when county officials suggested putting a garbage landfill in the town, a Potomac resident named Ralph Reed immediately became worried that the landfill would attract scavenger birds, which might collide with jet airplanes taking off from National Airport. Reed was a former aerospace engineer with United Airlines who at the time was staff director of the House of Representatives' subcommittee on transportation and aviation.

When he heard about the proposed landfill, he began calling his friends, who included officials of the Federal Aviation Administration, the Aircraft Owners and Pilots Association, and the Air Transporter Association. At a hearing on whether to grant a permit for the landfill, pilots from these agencies testiied to the danger of birds and planes colliding, persuading the judge to refuse granting the permit -- and the landfill.

Preserving Parklands: One way Potomac has managed to keep 27.8 percent of its land undeveloped is to persuade county officials to buy it for parks.

For example, any time that a landowner decides to sell land along Potomac's Seneca Creek, the county council purchases it, saying that the county government must protect the precious stream valley from developers. But the council does not always purchase land along Sligo Creek, at the eastern end of the county, where families of low and moderate income live. In fact, the county government wants to use some of the land it owns along Sligo Creek for subsidized housing for low and moderate income families.

The Public Relations Blitz: If all else fails, Potomac takes its case to the newspapers.

A few weeks ago, for example, Nancy Kogan, president of the McAuley Park Citizens Association, figured she might be able to keep the U.S. Postal Service management school out of Potomac if she could get people across the country angry about the amount of money that the Postal Service was spending -- $6.5 million for the land and about $30 million for new structures.

Kogan phoned newspaper reporters and radio stations, telling them about the "enormous boondoggle" that the Postal Service was going to provide for its workers.

Then she got more specific. "If you could," she told one reporter, "write the first paragraph of the story saying, "An all-expense paid, four-week vacation in beautiful Potomac is about to become a reality for hundreds of Postal Service workers."

Kogan added that she would like the story to run on a Sunday, when the newspaper's circulation is wider, and that she would like the story to move on the newspaper's wire service so people throughout the country would see it. If it didn't run on the wire, she said, she knew someone who could make sure that it did.

Although Kogan was anxious to alert people to the cost of the Postal Service school, her reason for opposing the school had more to do with its prospective students than economics.

"I doubt they'd stay on the campus the whole time," Kogan said, referring to the students. "They probably like jogging and some of them would be wandering around to see the neighborhood. Strange men walking into the streets are not desirable."

But all of Potomac residents' tactics would not do them much good if it were not for the clout they have with the man in charge of planning for Montgomery County, Royce Hanson, the executive director of the Maryland National Capital Park and Planning Commission.

Hanson, who lives in Potomac, believes that "it makes good sense" to keep Potomac an area of enormous houses on wide lots, devoid of the blights most other communities have, like fast-food restaurants and halfway houses.

"There are areas in almost all counties," said Hanson, "where people who buy land can insulate themselves from people who aren't as well off or live in smaller houses. Potomac is such an area."

Of the seven council members, four regularly take the recommendation of Hanson's planning board on rezoning decisions.

Nevertheless, Potomac residents worry about the fact that there is less and less undeveloped land.

In recent years, for example, developers have built large, expensive houses over portions of the "horse beltway," the bridle path around Potomac. They also plan to build imposing houses on the former sites of the Potomac steeplechase course and the Potomac polo fields.

Last year, the headquarters of the Potomac Hunt was sold to developers, forcing Potomac's foxhunters to mount their horses in nearby Darnestown each fall and winter.

When asked, Potomac residents are candid about their reasons for fighting to keep Potomac a neighborhood of wide lots and enormous houses. "We aspire," said Aron, president of the West Montgomery Civic Association, "to something better."

Marcia Airis believes it is good for the entire county that a place like Potomac exists. "There should be a variety of living environments in the county," Airis said. "People move here because of the open space. If we lose the open space, we lose something in terms of our values."

But residents of other parts of the county do not think it is quite fair that so much of the county's open space -- both public and private -- is in Potomac.

"Some areas of the county have no way to insure that they have the basic minimum of things that make life pleasant," said County Council member Rose Crenca, who lives in Takoma Park. "Children in every part of the county deserve the opportunity to have streams and open space, but in some parts of the county those things just aren't there." CAPTION: Picture 1, no caption; Picture 2, Civic Association members are Marcia Airis, Ruth Ann Aron, Mary Anne Thane. By James A. Parcell -- The Washington Post; Map, no caption, by Alices Kresse